In industry and biology it is often advantageous to capture particulate material suspended in a liquid or gas, on a filter for purification, enrichment, observation or subsequent analysis. The quantity and characteristics of particulate material is important in manufacturing, for example, processes that utilize powders, pigments, fuels or lubricants. Particle evaluations are also used to assess contaminants in water or air such as pollen, asbestos and soot. Particulate material is sometimes used indirectly to assess proteins or chemicals, for example, beads coated with monoclonal antibody may be interacted with blood. Then these beads may be captured on a filter and assessed for bound protein.
As used herein, “sample suspension” means particulate material suspended in a liquid or gas. “Material” as used herein means biological cells, organisms, bacteria, viruses, or components of these, as well as organic and inorganic particulates or any other matter which may be captured or isolated on a filter. This captured material may be subsequently used to provide diagnostic and/or analytical information or be re-suspended or otherwise used. For example, captured material may be analyzed chemically or may be placed on a receiving surface, such as a microscope slide for analysis.
Although there are a number of established methods to deposit mono-layers of material on a receiving surface for observation or analysis, controlling the amount of material collected on a filter is more difficult to achieve. Typically, electronic control and intervention is required to monitor and control the collection of material on a filter apparatus and/or other laboratory methods (employing particle counters and dilution techniques) are used to adjust the concentration of the material in suspension. Unfortunately, these methods require additional apparatus and electronics, and are relatively complex or expensive in terms of supplies, and time. Therefore, a simple, reliable method of capturing a desired amount of material on a filter would be advantageous.
The present invention is a filter device that provides a means to collect a desired amount of material. To accomplish this, a pressure sensor is used substantially to monitor the flow rate through the filter. In addition, the pressure sensor may be combined with a valve that provides control over sample flow, and thus the collection of material. In one embodiment of the present invention, a pressure sensor and valve are integrated to form a pressure-sensitive check valve. In other embodiments the membrane filter or filter assembly themselves deform, acting as a pressure sensor and flow control mechanism.